Hymenocephalus nascens Gilbert & Hubbs 1920

Hymenocephalus nascens Gilbert & Hubbs 1920

Nascent membranehead

(Figures 3, 8)

Hymenocephalus nascens Gilbert & Hubbs, 1920: 535, Fig. 33 (Holotype: USNM 78229, vicinity of Sibuko Bay, Borneo, Albatross station 5587, depth 415 fathoms [759 m]).

Hymenocephalus nascens: Iwamoto, 1990: 230 (listed). Iwamoto & Merrett, 1997: 523 –525, fig. 22b (New Caledonian region). Iwamoto & Williams, 1999: 177 –178 (Western Australia). Iwamoto, 1999: 1991 (listed). Merrett & Iwamoto, 2000: 759, fig. 20 (Vanuatu, New Caledonia). Iwamoto & Graham 2001: 475 –476 (New South Wales). Bray et al. 2006: 596. Hymenocephalus sp. B: King et al., 2009: 531.

Diagnosis (New Zealand specimens only). Pelvic rays 12–14 (elsewhere 11–13), total gill rakers first arch (outer/ inner) 17–22/23–28, second arch 22–28/22–26, chin barbel absent, orbit diameter 29–40% HL, suborbital width 10–14% HL, snout length 22–31% HL, interorbital width 24–29% HL. Most of orbit, upper surface of snout, sides of head and trunk silvery or pale, ventral aspects of head and trunk black. Prominent mid-lateral stripe of silvery (fresh) or brownish (preserved) pigment running along trunk and tail.

Specimens examined (20: 15–33.4 mm HL, 66–182 mm TL, New Zealand only). NMNZ P. 0 18040 (25.2 mm HL, 122+ mm TL), North Island, RV James Cook, (data uncertain, might be JCO8405/032, Challenger Plateau), bottom trawl. NMNZ P.023552 (7: 28.3–33.3 mm HL, 103+–172+ mm TL), off 90 Mile Beach, 34º 51.3' S, 172º 3.1' E, 894– 876 m, RV James Cook, JCO8106/057, bottom trawl, 24 Apr 1981. NMNZ P. 0 23553 (30 mm HL, 182+ mm TL), off Cape Runaway, Bay of Plenty, 37º 27.1' S, 177º 42.8' E, 815–843 m, RV James Cook, JCO8106/ 0 18, bottom trawl, 17 Apr 1981. NMNZ P. 0 23554 (33.4 mm HL, 136+ mm TL), NE of North Cape, 34º 11.7' S, 173º 7.1' E, 903–975 m, RV James Cook, JCO8106/044, bottom trawl, 22 Apr 1981. NMNZ P. 0 34688 (4: 15–28.4 mm HL, 66+–150+ mm TL), off Napier Island, Kermadec Islands, 29º 13' S, 177º 52.4' W, 610 m, NZOI station K0829, trawl, 0 6 Jul 1974. NMNZ P. 0 34689 (26.4 mm HL, 126+ mm TL), Southern Lau Ridge, Tonga, 25º 13.7' S, 179º 4.1' W, 646 m, NZOI station P0947, 0 1 Jun 1980. NMNZ P. 0 34714 (3: 25.5–28 mm HL, 116+–132+ mm TL), east of Dayrell Island, Kermadec Islands, 29º 14.8' S, 177º 49.6' W, 590 m, NZOI station K0804, 0 2 Jul 1974. NMNZ P. 0 34717 (26.4 mm HL, 154 mm TL), off Bay of Islands, 34º 43.5' S, 174º 31.5' E, 743 m, RV NZOI station F0913, 0 1 Oct 1968. NMNZ P. 0 39620 (32.4 mm HL, 157+ mm TL), Southern Norfolk Ridge, New Zealand EEZ, 34º 34.5' S, 168º 57.2' E, 813–1000 m, RV Tangaroa, NORFANZ TAN0308/155, wing trawl, 0 4 Jun 2003.

Description (Counts and proportional measurements are presented in Table 3). Gilbert and Hubbs (1920:535) and Iwamoto & Merrett (1997:524) provide detailed descriptions of this species.

Colour. Head mostly pale but anterior margin of upper and lower jaws blackish. Brownish stripe of pigment above mid-lateral line from behind head, running along tail but fading posteriorly. Trunk and tail below mid-lateral line pale, peppered with small melanophores. Silvery-blackish ventral striae on isthmus and chest midway between pelvic fin bases and anal fin origin. All fins pale-dusky.

Size. To about 33 mm HL and 182 mm TL.

Distribution (Figure 10). In the New Zealand region known from Challenger Plateau, off 90 Mile Beach (west coast North Island), north of about East Cape on the east coast North Island, southern Norfolk Ridge, and off Kermadec Islands; 590–1000 m. Elsewhere widespread in tropical west Pacific from South China Sea off Hong Kong, Philippines and Indonesia, off northeast Australia to New Caledonia (Iwamoto & Merrett, 1997), and Southern Lau Ridge (Tonga region).

Comparisons and remarks (Table 3). This species is widespread and its presence in northern New Zealand waters is not surprising. The combination of absence of a chin barbel, 12–14 pelvic fin rays and distinctive midlateral silvery stripe running along the trunk and tail distinguishes this species from others in the genus. Iwamoto and Merrett (1997:524) summarised data for specimens taken from the New Caledonia region, and we have compared New Zealand and New Caledonia specimens in Table 3.